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XR400 Mikuni Pumper Install - custom bracket

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I thought I had a direct bolt-on Mikuni Pumper carb for my XR400... however, I was incorrect in my assumptions. Here's what I had, and had to do to correct the install;

I bought a carb from Buckrun, which he had mentioned it came off an XR4. "No prob" I figured, should be a cinch to install. He even had what he mentioned as "new" cables "in the bag", but they looked used and were not in a sealed bag or manufacturer bag of any sort... so I'm not sure what they came off of, or if they had been used with any bike or carb.

I took the cables out, and inspected them... noticing that the side for the throttle tube didn't have the correct barrel end on the cable. It was a ball end. Not sure I could have used those or not. The carb end is the side that looked used, and dirty... corroded a bit, but they would have fit the mount to the Mikuni. Once I checked length on them, I realized with my forward mounted GPR Stabilizer post, I wanted to use my +3" longer cables. This in itself would cause part of my problems with the install.

The carb itself came without an idle adjustment, so I made one. Not too shabby... sadly, I ended up taking it out as the carb wouldn't fit on the bike with it installed. Darn it... on with the install, worry about "idle" later.

I also changed the jetting to a 130/15. As it came to me with 125/12.5 - seemed to be the right combo.

I soon noticed that my cables would be too long at the carb. The outer covering was okay, just my free length on the cables was far too long. So I measured once, twice and a third time before I cut off the Mikuni cable mount. I then proceeded to take the cable mount off the stock carb and drill it out to mount to a custom bracket I made. That stock mount, must be some kind of hardened steel... amazingly, I had no drills that could easily get a hole drilled, without some kind of trouble. I tapped the holes in the custom bracket I made, and planned on backing up the bolts with nylocs. I don't want it coming loose on the trail!

I mounted the custom bracket to the carb using a longer bolt than stock, and then mounted the stock carb bracket to my custom mount. Basically extending out the stock mount and taking up the slack on the cables. WHA-LA... done.

I bolted the carb on, and started it up... NOT on the first kick however, about 30 kicks later (due to some fuel starvation issues since I didn't bolt on my tank to get it going - long story). It purred along, but with a high idle. See, I had screwed a small bolt into the idle assembly just to make sure I could adjust it to test and have "some idle adjustment". And once started, I pulled the idle all the way out... and it seemed to run okay without any idle screw at all. (anyone else run with an idle assembly installed?!).

I took the air/fuel screw out to 2.5 turns, and played with the enrichener a bit... and it idled just fine. In fact, it runs great.... took it out for a spin and it's a nice touch. Not sure on the power delivery, and if it's more or not... as my stock carb was a first kick hot or cold, and ran perfect already. I'm eager to test it out on the open desert, in the whoops, and everywhere else I'll be next week (in the dez for 4 days).

Thanks to Buckrun for the carb! ๐Ÿ‘

Here's the pictures of the foiled idle screw, and my working cable mount;






Edited by johnnyairtime
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Nice work around.

Tell me you didn't leave the top cable loose in the bracket as shown in pic#5.

๐Ÿคฃ ... I sure did. And had to go back, after installing the tank and seat. I realized it when I posted the pics ๐Ÿ‘ It's the second time I've done that! ๐Ÿ™‚

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Awfully nice of you to do all that extra work and STILL thank the guy that wasn't very honest with you.

(you must be a nice person) :jawdrop:

That... and it was a bit sarcastic. ๐Ÿ™‚ And I don't try to make things more than they are, so I just rolled with it and did the install. No worries.

He-He, is that "three" brackets screwed together... I thought you had a welding machine.


:applause: ... Mig, Tig, Oxy, and a plasma cutter (plus a nice tube bender - but hey, who's counting ๐Ÿ‘). But they're all buried behind a CR500. Okay... not "buried" per-say... it was just easy enough to bolt together rather than TIG the bracket. In fact, I was all too prepared to pull the TIG out when I realized it held damn strong with it bolted together. I was going to use the TIG to final secure it in place... but, I don't think it was necessary.

... trust me, I stared at the idea(s) long enough to nearly mind-melt the steel together. I had several different methods working, and did all this without removing the stock Mikuni bracket. If I was to remove it, then I'd probably have MIG'd the brackets together and skipped my custom tab extending out the stock bracket. I just didn't plan on making it an ALL day affair.

You don't like my sammwich?๐Ÿคฃ

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Yes this jetting was on my stock motor.It did have,airbox mods,big tube header,with big gun muffler,with welded turn down on muffler to make it stealh.My 440,mild cam,same jetting.The trick to that motor is in the airbox and pipe.If your motor handles the bigger jets then you know it flows better,then one with small jets.Being they are rode in the same place.

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